MADRID (AP) -- Serena Williams overcame a sluggish start to beat Caroline Wozniacki 1-6, 6-3, 6-2 Thursday and reach the Madrid Open quarterfinals.

Williams hit the net on three straight points in her opening service game and then didn't put up much resistance in the rest of the of the first set. But she broke Wozniacki at love in the fifth game of the second and ripped a forehand return winner for another break that put her ahead 4-3.

Wozniacki had no reply as the Dane hit a shot long to go down 2-0 in the decider, and Williams cruised to victory in a matchup of former top-ranked players.

Williams improved her record to 10-0 on clay this season with her third win on Madrid's unorthodox blue-clay surface.

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